1. Field of the Invention
The present invention relates to a semiconductor laser device capable of selectively emitting two kinds of laser light different from each other in wavelength, emission point, beam shape, emission power, longitudinal mode and so on, by switching the direction in which a voltage is applied to the device.
2. Description of the Background Art
A semiconductor laser device is widely employed in optical information recording apparatus such as a CD player, a DVD player and so on. In particular, the semiconductor laser device employed in the optical pick-up is differently manufactured depending on the requested information recording density or the like of the optical information recording apparatus. For example, an infrared semiconductor laser device of a wavelength of 780 nm is employed for a CD player, a red semiconductor laser device of a wavelength of 650 nm is employed for a DVD player, and a blue semiconductor laser device of a wavelength of 410 nm is employed for an improved type DVD player, or a HD-DVD player in which information recording capacity per unit area is increased.
As shown in FIG. 1, a conventional ridge type semiconductor laser device employed in an optical pick-up is formed of a multilayer structure body in which, for example, a substrate 101 has an n-type semiconductor layer 102, n-type semiconductor cladding layer 103, an active layer 104, a p-type semiconductor cladding layer 105, a p-type semiconductor contact layer 106 deposited thereon in this order. Then, a p-type electrode 107 and an n-type electrode 108 are formed on the p-type semiconductor contact layer 106 and the n-type semiconductor layer 102, respectively.
According to the semiconductor laser device of the structure, if the material of each layer, the thickness of the same and so on are properly selected, it becomes possible to vary the light emission characteristic of the oscillated laser wavelength or the like. For example, if an AlGaAs system material is selected for the semiconductor layers, the laser device will oscillate at a wavelength of an infrared range near 780 nm, if an AlGaInP system material is selected for the same, then the device will oscillate at a wavelength near 650 nm, and if a GaN system material is selected for the device, the device will oscillate at a wavelength of near 400 nm.
The above-described semiconductor laser device oscillates only at a predetermined single wavelength. Thus, a compatible player, which is designed for reproducing both of the CD and DVD employs a reproducing mechanism described as follows. That is, 1) the compatible player is equipped with a plurality of pickups each having a semiconductor laser device designed to cope with each kind of optical disk, whereby reproduction operation is carried out, 2) a plurality of semiconductor laser devices each having different wavelength are arrayed within a single optical pick-up package and a laser device is selectively energized for light emission for each optical disk, thus carrying out the reproducing operation.
However, according to the scheme of 1), it is necessary to provide a drive mechanism for each pick-up, with the result that the apparatus becomes large and manufacturing cost is increased. According to the scheme of 2), light emitted from a plurality of laser devices shall be optically coupled to a single lens of the pick-up. Therefore, the emission spots of the laser devices should be sufficiently close to each other, whereby the manufacturing process includes a very cumbersome step of positioning each laser device with high accuracy on a substrate, which fact also causes cost increase.
As has been described above, it is desired to provide a semiconductor laser device capable of emitting laser light of a plurality of wavelengths by use of a single semiconductor device without a plurality of semiconductor devices each emitting laser light of a single wavelength are arrayed.
Further, it is desired to provide a semiconductor laser device having a single device arrangement which is capable of emitting various laser light differing in not only wavelength but also light emitting point, beam shape, emission power, longitudinal mode and so on.
Therefore, it is an object of the present invention to provide a semiconductor laser device capable of emitting laser light of a couple of different light emitting characteristics as described above. Also, it is an object of the present invention to propose a fabricating method thereof.
According to the present invention, there is provided a semiconductor laser device including first and second laser units, each having a ridge type structure and each comprising a multilayer structure body made up of at least an n-type semiconductor layer, an active layer and a p-type semiconductor layer deposited in this order, and a p-side electrode and an n-side electrode, wherein the p-side electrode and the n-side electrode of the first laser unit and the n-side electrode and the p-side electrode of the second laser unit are electrically connected, respectively.
Further, according to the present invention, there is proposed a method of fabricating a semiconductor laser device including a laser assembly forming step composed of a step for forming a multilayer structure body having at least an n-type semiconductor layer, an active layer and a p-type semiconductor layer deposited on a substrate, a step for partly removing a top portion of the multilayer structure body so as to expose the n-type semiconductor layer, thus forming a ridge in a stripe fashion, and a step for forming a first electrode on the top portion of the ridge and a second electrode on the n-type semiconductor layer at a position lower than the top of the ridge, a step for preparing first and second laser assemblies by repeating the laser assembly forming step, a step for bringing the first laser assembly and the second laser assembly into registration with each other so that the first electrode and the second electrode of the first laser assembly are brought to opposition to the second electrode and the first electrode of the second laser assembly with a fusing material interposed therebetween, a step for intimately attaching the first and second laser assemblies with each other and melting the fusing material to bond the first and second laser assemblies together, a step for removing at least the substrate of insulating property from the first and second laser assemblies, and a step for forming an electrode on the bottom of the n-type semiconductor layer of the first and second laser assemblies.